Development apparatus

ABSTRACT

APPARATUS TO CONTROL THE STOPPING AND STARTING FUNCTION OF A MAGNETIC BRUSH DEVELOPING SYSTEM IN WHICH THE MAGNETIC BRUSH IS RAPIDLY BROUGHT IN AND OUT OF OPERATIVE CONTACT WITH AN IMAGE BEARING PHOTOCONDUCTIVE SURFACE.

March 23, 1971 1.. H. TURNER 3,572,288

DEVELOPMENT APPARATUS Filed Aug. 7, 1968 3 Sheets-Sheet l IN VENTORSLYMAN H. TURNER ATTORNEY March 23, 1971 3 Sheets-Sheet 2 Filed Aug. 7,1968 NR MK v MC V 1 F & T Sw S W 0 l mm Q mm w @R g m \m a mm mm 1| .v I1 1 m Q Q F m mm nw m mm R mm vw March 23, E971 L. H. TURNER 3,572,283

DEVELOPMENT APPARATUS Filed Aug. 7. 1968 3 Sheets-Sheet 5 United StatesPatent 3,572,288 DEVELOPMENT APPARATUS Lyman H. Turner, Pittsford, N.Y.,assignor to Xerox Corporation, Rochester, N.Y. Filed Aug. 7, 1968, Ser.No. 750,851 Int. Cl. B05b 5/02 US. Cl. 118-637 4 Claims ABSTRACT OF THEDISCLOSURE Apparatus to control the stopping and starting function of amagnetic brush developing system in which the magnetic brush is rapidlybrought in and out of operative contact with an image bearingphotoconductive surface.

This invention relates in general to development of a latentelectrostatic image and, in particular, to a magnetic brush developingapparatus the development function of which can be rapidly started orstopped.

In the process of xerography, as originally disclosed by Carlson in US.Pat. No. 2,287,691, a plate comprising a conductive backing upon whichis placed a photoconductive insulating material is charged uniformly andthe photoconductive surface exposed to a light image of an originaldocument to be reproduced. The photoconductive coating is caused tobecome conductive under the influence of the light image so as toselectively dissipate the electrostatic charge found thereon producingwhat is known as a latent electrostatic image. The latent image isdeveloped, or made visible, by means of a variety of pigmented resinswhich have been specifically developed for this purpose. The pigmentedresin material, commonly referred to as toner, is electrostaticallyattracted to the latent image on the photoconductive surface inproportion to the amount of charge found thereon. That is, an area ofsmall charge concentration becomes an area of low toner density whileareas of greater charge concentration become proportionally more dense.The developed image is generally transferred to a final supportmaterial, as for example paper, and fixed thereto to form a permanentrecord of the original document.

The principal mechanism for developing the latent electrostatic image inthe xerographic process is by means of the classicaldevelopment-scavenging technique utilizing two-component developer.Two-component developer comprises a finely divided toner material and arelatively coarser carrier material. Opposite electrostatic charges areinduced in the materials when they are brought into rubbing contact. Theoppositely charged toner is attracted to the larger carrier until suchtime as the carrier becomes electrostatically satisfied. To develop alatent electrostatic image, as for example on a photoconductive surface,the loaded developer material is caused to flow over the photoconductivesurface whereby the toner is mechanically and electrostaticallydislodged from the carrier material. The latent electrostatic imageexerts a force on the toner material and the toner is attracted into theimage areas to selectively develop the image in relation to the amountof charge found thereon. The denuded carrier material, still possessinga charge opposite to that of the toner, seeks to scavenge toner awayfrom the electrostatically relatively weak non-image or background areasresulting in the formation of a clean, sharp, visual reproduction of theoriginal document.

The two primary methods of developing a latent electrostatic image usinga two-component developer material are magnetic brush development andcascade development. In both these development systems, sufficient fiowmust be maintained within the system to produce proper mixing andtri'boelectrification of the materials.

"ice

Because two-component developer systems are flow-dependent, it is theusual practice in automatic xerographic machines to continually operatethe developer system any time the machine is in use such as when amultiple copy run is being made.

In automatic xerography the photoconductive surface is generallycontinually charged and intermittently imaged. The continuous operationof the developer system has heretofore not been a serious problem inautomatic xerography because the equipment Was insensitive to the lowdensity charge fields found between copies and this area was notdeveloped. However, with the advent of new xerographic developingmaterials and proc essing techniques, it is now possible to developsolid areas of relatively uniform charge density on a photoconductivesurface. Automatic machines having this good solid area capability,unless controlled in some manner, will produce unwanted development ofthe charged but non-imaged solid areas between copies. This unwanteddevelopment results in excessive toner consumption in the machine aswell as producing a high level of dirt. Furthermore, because thisunwanted development is not transferred to a final support material itmust in some manner be cleaned from the photoreceptor which poses aserious residual toner cleaning and handling problem.

It is therefore a primary object of this invention to improve apparatusfor developing a latent electrostatic image in automatic xerographicmachines and in particular machines having a solid area developmentcapability.

Another object of this invention is to provide a twocomponent developingapparatus having the capability of being rapidly started and stopped.

Yet another object of this invention is to reduce the dirt level and theamount of cleaning required in an automatic xerographic machine havingsolid area capabilities.

A still further object of this invention is to eliminate unwanteddevelopment of charged but non-imaged areas in an automatic xerographicmachine having solid area capabilities.

These and other objects of the present invention are attained by meansof a housing adapted to support a quantity of magnetizable developermaterial having an opening at the top thereof, means to produce adirectional flux field capable of passing through the opening in the topof said housing, the flux producing means being movably positioned insaid housing between a first developing position and a secondnon-developing position, a hollow applicator roll being arranged tocontain the flux producing means and adapted to pass through thedeveloper material in the housing and the main flux field, rotatingmeans to move the applicator roll through the developer material and themain flux field so that a brush of developer material is continuallymaintained in said flux field, means to reposition the flux producingmeans within the applicator roll from a first developing position to asecond non-developing position, and means to collapse the brush when inthe non-developing position.

For a better understanding of this invention as well as other objectsand further features thereof, reference is had to the following detaileddescription to be read in connection with the accompanying drawings,wherein:

FIG. 1 illustrates schematically an embodiment of the instant inventionin an automatic Xerographic reproducing apparatus;

FIG. 2 is a front elevation in partial section showing the developmentapparatus of the instant invention;

FIG. 3 is a right-hand end view of the development apparatus shown inFIG. 2;

FIG. 4 is a left-hand end view of the development apparatus shown inFIG. 2;

FIG. is a left-hand sectional view of the development apparatus takenalong lines 5-5 of FIG. 2 showing the flux producing means in adeveloping position;

FIG. 6 is a partial sectional view of the development apparatus as shownin FIG. 5 with the flux producing means in a non-developing position;

FIG. 7 is a partial top view of the development apparatus taken alonglines 7-7 of FIG. 5.

In the illustrated embodiment of the instant invention a developerhousing 14 is shown in an automatic xerographic reproducing machine. Thexerographic apparatus comprises a record receiving member in the form ofa xerographic drum 10 rotatably mounted in the machine frame by means ofshaft 11. The drum is rotated in the direction indicated by the arrow tocause the drum surface to pass sequentially through a plurality ofxerographic processing stations.

For the purpose of the present disclosure, the several xerographicprocessing stations in the path of movement of the drum surface may bedescribed functionally as follows:

A charging station A, at which a uniform electrostatic charge isdeposited on the photoconductive surface of the drum and includes acorona charging device 12 having a corona discharge area of one or morecorona discharge electrodes that extend transversely across the drumsurface and are energized from a high potential source;

An exposure station E, at which a light or radiation pattern of the copyto be reproduced is projected onto the drum surface by means ofprojector 13 to dissipate the charge on the drum surface in the exposedareas there of to form a latent electrostatic image of the original tobe reproduced;

a developing station C, having a magnetic developing system 14 driven bymeans of motor 22 through chain 23 in which two-component magnetizabledeveloping material is caused to flow in contact with the drum surfaceso that the toner brought in contact therewith adheres to the latentimage to form a powder image of the original document to be reproduced;

A transfer station D, at which the xerographic powder image iselectrostatically transferred from the drum surface to a web 15 of finalsupport material by means of a corona discharge device 16 similar to thecharge device positioned at the exposure station; and

A drum cleaning station E, at which the drum surface is brushed by meansof a natural or synthetic fur brush 20 to remove residual tonerparticles remaining on the photoconductive surface after image transfer.

The web of support material is held in contact with the drum surface bymeans of a pair of idler rolls 19. The web is adapted to move at thesame peripheral speed as the drum surface by means of a motor acting ontake up spool 17. The take up spool, in turn, acts to pull or move acontinuous supply of support material from freely rotating supply spool18 through the transfer station D. A fuser assembly 21 is positioned inclose proximity to the moving support material subsequent to thexerographic transfer station. Sufiicient heat energy is provided by thefuser assembly to fix the xerographic toner images to the final supportmaterial as the image is passed thereunder.

It is believed that the foregoing description is sufficient for thepurposes of this application to show the general operation of axerographic reproducing apparatus. However, as will be explained ingreater detail below, the magnetic brush developer system as hereindisclosed is not limited to this particular xerographic device andbecause of its novel features is applicable in a wide range of machinesand environments.

The development apparatus of the present invention includes a maindeveloper housing, generally designated 30, comprising a main shell 31which is closed at both ends by means of end plates 32 and 33. The mainshell of the housing is basically a U-shaped elongated trough-likemember in which the bottom section thereof is inclined in relation tohorizontal plane. The elongated trough-like area of the main housing isbroken into two distinct areas by means of separator plate 34. Thehousing is divided into a main developer area 35, which is slightlylarger than the photoconductive area on the drum surface, and a secondsupply or reservoir area 36.

The main housing is supported in machine frame 8 by means of two supportpads 37 and 38 securely bolted to the machine frame. End plate 33 anddivider plate 34 extend below the bottom portion of the developerhousing and have horizontal dependent flanges thereon adapted to besecurely mounted upon support pads 37 and 38, respectively. Thedeveloper housing is supported in the machine frame so that the maindeveloper area within the housing is in close proximity andsubstantially transverse to the lower portion of drum surface 10.

Positioned in the lower sump portion of the trough are two screw typeaugers generally designated 40 and 41. The augers are rotatablysupported in bearings, such as fiber bearings, mounted in the end platesof housing 30-. Helical feed screws 42 and 43 associated with augers 4t)and 41, respectively, are positioned in parallel relation to each otherrunning substantially across the full length of the bottom of thehousing. Openings are provided in the divider plate to permit the augersto transport developer material between the reservoir area and the mainde- Weloper area. Delivery auger 40, positioned at the higher elevationin the housing, is rotated in the manner such that feed screw 42continually moves a flow of developer material from the reservoir areainto the development zone while the lower or return auger 41 transportsdeveloper material from the developer zone back into the reservoir area.

The shaft portion of augers 41 and 40 extend external end plates 33having pinion gears 78 and 79, respectively, securely mounted on theterminus end thereof (FIG. 3). The two pinions are driven from a commondrive gear mounted on stub shaft 81 rotatably supported in the maindeveloper housing. The mechanical action of the augers against thedeveloper material provides sufficient agitation within the developermaterial to produce mixing and triboelectrification for thetwo-component xerographic development.

Positioned in the upper portion of the developer area within thedeveloper housing is an applicator roll, generally designated 50,extending substantially across the length of development area 35.Applicator roll 50 comprises a hollow cylindrical non-magnetic sleeve 51supported between end caps 52 and 53 and the end caps suitably mountedfor rotation in divider plate 34 and end plate 33.

Mounted within the applicator roll sleeve 51 is a permanent magnet 68constructed of Alnico 5 or other similar magnetic materials. The magnetconsists of an elongated north pole piece 60 and equally long elongatedsouth pole piece 61 separated by insulating strip 62. The two polepieces are positioned in relatively close proximity to each other withinthe applicator sleeve so as to create a main magnetic flux field 45which is substantially directional. The length of the magnet is slightlylonger than the width of the photoconductive area on the recordreceiving surface and is positioned so that the main flux field extendsat least as long as the photoconductive area on the drum. Although anelongated permanent magnet is shown in this embodiment it should bequite clear that any other type of magnet capable of producing asubstantially directional flux field would be perfectly suitable for usein the instant invention.

Magnet 59 is rotatably supported within applicator roll sleeve 51 sothat the magnet can be turned independently of the applicator roll. Theright-hand end of the magnet, as shown in FIG. 2, is supported upon stubshaft 63 which is rotatably mounted in end cap 53 by means of rollerbearings 64. The extended shaft is supported between roller bearing 64,pressed in end cap 52, and bearing blocks 66 affixed in the housing endplate 32. A portion of shaft 65 extends beyond the housing and hassecured thereto a lever arm 88, the function of which will be explainedin greater detail below.

Stub shaft 81 which drives the delivery and return augers also acts asthe main drive shaft for the developer unit. A sprocket 6'5 pinned toshaft 81 transmits the rotational motion delivered from motor 22 throughchain 23 to the shaft. A timing pulley 72, also affixed to stub shaft81, acts through timing belt 73 to drive the applicator roll drivesystem 56. As shown in FIG. 2, the applicator drive system comprises anelectromagnetic clutch 71 operatively connected to driven timing pulley70. Applicator roll 50 is operatively connected to applicator drive rollassembly 56 by means of coupling 55.

In operation, a continuous flow of developer material is moved from thereservoir area 36 through the development area 35 by means of therotating delivery and return angers. The rotational speed of the augersis maintained at a level high enough to produce sutficient mechanicalagitation to properly mix and triboelectrify the developer material. Thedeveloper housing is charged with sufficient developer material so thatthe applicator roll is partially immersed in the developer material. Theapplicator roll is immersed sufficiently within the bath of developermaterial so that the fringe areas of the directional magnetic flux fieldassociated with magnet 59 are felt by the developer material in thehousing. The applicator roll as it rotates through the bath of developermaterial, brings developer material into the main flux field associatedwith magnet 59 by magnetic and mechanical forces. As the applicator rollmoves through the developer material, the mag-netizable particles underthe influence of the magnetic flux field are caused to move upwardlyinto the main flux field to form What is commonly referred to as amagnetic brush. As shown in FIG. 5, the upper delivery auger moves afresh supply of magnetic developer material transverse to the applicatorroll in close proximity to the brush forming area. As the applicatorroll continues to rotate the developer material in the brush is causedto move downwardly back into the sump area of the developer housing. Inthis manner a magnetic brush is continually being formed from freshdeveloper material as it circulates through the system.

Referring now to FIG. 6 the rotatable magnet is shown positioned in adeveloping position. Development of a xerographic image is produced ondrum surface 10 by directing the main flux field 45 of the magnettowards the drum surface. The applicator roll, and therefore the magnetcontained therein, are supported within the developer housing so thatthe photoconductive area on the drum surface is caused to pass throughthe main flux field when the magnet is in the developing position asshown in FIG. 6. Magnetic brush 44 continually carries a flow of freshdeveloper material into contact with the photoconductive surface todevelop a latent electrostatic image thereon. The peripheral speed ofthe applicator roll, and therefore the flow rate at which the magneticbrush is replenished, and the speed of the xerographic drum are relatedthrough the integrated drive system so that uniform application ofdeveloper material is produced there- In order to rapidly start and stopthe development function of the present development apparatus, themagnet is rotated or repositioned from a first developing position inwhich the main flux field is directed toward a photoconductive surfaceand a second non-developing position in which the field is directed awayfrom the surface. The magnet, which is free to rotate independentlywithin the applicator roll, is repositioned by means of solenoid SOL-1mounted on bracket 44 afiixed to end plate 32 of the housing. Shaft 65,connected to the elongated magnet terminates in level arm 88 which isoperatively connected to the actuator arm 87 of solenoid SOL-1. Leverarm 88 has a slotted hole 90 machine therein in which pin 89, associatedwith lever arm 87 of SOL-1 rides. Lever arm 88 is biased into contactwith lever arm 87 by means of spring 91 (FIG. 4).

In the magnetic brush apparatus herein described, as in most devicesemploying two-component developer materials, a powder cloud consistingof free toner material may be formed in the vicinity of thephotoconductive surfaces. The powder cloud generally is formed by tonerdislodged from the carrier material due to the mechanical interaction ofthe moving brush and the moving photoconductive surface. As can be seen,this free toner is available to develop a latent electrostatic image onthe photoconductive surface. Because this powder cloud developer is notdirectly related to the brush position, repositioning of the brush alonemay not in itself produce an extremely rapid cessation of thedevelopment process, especially in high speed apparatus. Powder cloudsformed in the vicinity of a photoconductive surface should therefore besuppressed.

When the development apparatus of the instant invention is in a normaldevelopment condition, the solenoid actuator arm is raised causing thelever arm 88 associated with the magnet positioned device to assumeapproximately a horizontal position as shown in FIG. 6. The magnet,which is securely affixed to shaft 65, is being supported in asubstantially vertical direction with the main flux field directed atthe photoconductive surface. The magnetic brush is formed as heretoforeexplained and the latent image on the drum surface deve oped. Whensolenoid SOL-1 is electrically actuated the actuator arm is pulled downcausing the elongated magnet and associated flux field to assume thenon-developing position as shown in FIG. 5. That is, the magnet is in aposition in which the directional flux field is substantially pointedaway from the photoconductive surface. A brush collapsing arm 92,pivotally mounted in the main developer housing about pin 93, is at thesame time actuated and moves down into close proximity to the applicatorroll surface to break down the magnetic brush hairs thereby suppressingthe means by which a powder cloud could be formed in the vicinity of thedrum surface. Breaking down of the brush fibers also eliminates thedanger of stray brush hairs contacting and developing the drum surface.A collar 94 is securely affixed to shaft 65 and positioned adjacent toseparator plate 34 as shown in FIGS. 2, 5 and 7. A link 95, rotatablypinned to both the collar and the collapsing arm, moves with shaft 65 asthe shaft is rotated between the developing and non-developing positionso as to pull the collapsing arm downwardly into the magnetic brushhairs.

As noted, developer material is both mechanically and magneticallypulled from the sump area of housing 30. The mechanical action of theapplicator roll as it rotates through the bath of developer materialtends to agitate and mechanically drive developer material out of thebath towards the drum surface. This mechanical action of the applicatorroll upon the developer material also tends to produce a powder cloudcapable of developing unwanted .images on the drum surface regardless ofwhether the magnet is in a developer non-developed position. In thepresent invention, the applicator drive assembly 56 is provided with anelectromagnetic clutch 71 capable of engaging and disengaging theapplicator roll from the main drive system. In operation,electromagnetic clutch 71 (FIG. 2) .is electrically connected in serieswith the actuating mechanism of solenoid SOL1 so that when the solenoidis pulled downwardly to a non-developing position, the rotation of theapplicator roll is stopped.

As can be seen, the present apparatus has the capabilities of rapidlystopping and starting the development function of a magnetic brushdeveloping system, as for example between copies in an automaticreproducing machine, while still maintaining all the advantagesassociated with the classical xerographic development-scavengingprocess. The apparatus is capable of moving a continuous flow ofproperly mixed and triboelectrified developer material through thedeveloping apparatus thus maintaining the system at optimum developingconditions and still having the ability to control the developingfunctions. Without interrupting this fiow of material through thesystem, means are provided by which the magnetic brush and any powdercloud that may be associated there with is rapidly moved in and out ofdeveloping contact with the photoconductive surface.

While this invention has been described with reference to the structuredisclosed therein, it is not confined to the details set forth, and thisapplication ,is intended to cover such modificaions or changes as maycome within the purposes of the improvements of the scope of thefollowing claims.

What is claimed is:

1. Apparatus for developing a latent electrostatic image on aphotoconductive surface including an elongated housing being adapted tohold a quantity of magnetic developer material therein and having anopening positioned adjacent to the photoconductive surface,

means to produce a continuous flow of developer material through saidhousing,

a hollow applicator roll positioned in the opening in said housing sothat the applicator roll is partially immersed in the developer materialsupported in said housing,

a magnetic member supported within said applicator roll in a normallyfixed operative position producing a main flux field directedsubstantially towards the photoconductive surface and moveable to aninoperative position which directs the field in a direction angularlydisplaced from the photoconductive surface,

means to rotate said applicator roll through the developer material andthe main flux field to form a brush of developer material in the mainflux field contacting the photoconductive surface,

means to angularly displace said magnetic member to an inoperativeposition within said applicator roll whereby the brush of magneticmaterial is moved out of developing contact with the photoconductivesurface.

2. Apparatus for developing a latent electrostatic image on aphotoconductive surface including an elongated housing being adapted tohold a quantity of magnetic developer material therein and having anopening positioned adjacent to the photoconductive surface,

means to produce a continuous flow of developer material through saidhousing,

a hollow applicator roll positioned in the opening in said housing sothat the applicator roll is partially immersed in the developer materialsupported in said housing,

magnetic means supported within said applicator roll and being capableof producing a main flux field directed substantially towards thephotoconductive surface,

means to rotate said applicator roll through the developer material andthe main flux field to form a brush of deveolper material in the mainflux field capable of contacting the photoconductive surface,

means to reposition said magnet within said applicator roll whereby thebrush of magnetic material is moved out of developing contact with thephotoconductive surface, and

further means operatively connected with said brush repositioning meansto prevent further rotation of said applicator roll when said magneticbrush is moved out of contact with the photoconductive surface.

3. The apparatus of claim 2 wherein said means to prevent furtherrotation of said applicator roll is an electromagnetic clutchoperatively connected to said applicator roll and said means to rotatethe roll.

4. Apparatus to develop a latent electrostatic image on a recordreceiving member including ahousing having an opening therein adjacentto the photoconductive member, said housing being adapted to support aquantity of magnetic developer material therein,

a hollow non-magnetic cylindrical applicator roll rotatably mounted insaid opening and being partially immersed in said developer material,

an elongated magnet positioned within said applicator roll being capableof producing a main magnetic flux field substantially directed towardsthe photoconductive surface, said magnet being independently supportedfor rotation within said applicator roll,

drive means to rotate said applicator roll sequentially through thedeveloper material and the main flux field whereby a magnetic brush ofdeveloper material is continually formed, said brush being of a lengthcapable of contacting the photoconductive surface,

means to rotate said magnet within said applicator roll from adeveloping position wherein the magnetic brush is in contact with therecord receiving member to a second non-developing position wherein saidbrush is out of contact with said receiving member,

clutching means associated with said applicator drive means and beingoperatively connected to said last mentioned means to prevent futrherrotation of said applicator roll when the brush is moved to a secondposition.

References Cited UNITED STATES PATENTS 3,040,704 6/ 1962 Bliss 1186373,145,122 8/1964 Streich, Sr. 118637 3,167,455 1/1965 Laben et al.118637 3,176,652 4/1965 Mott et al 118-'6-37 3,392,432 7/1968 Naumann29-110 PETER FELDMAN, Primary Examiner US. Cl. X.R.

